Peru's former left-leaning president Ollanta Humala and his wife asked an appeals court on Monday to free them from jail where they have been ordered to spend up to 18 months before a trial over allegations they took illegal funds from Brazilian builder Odebrecht.

Humala and former first lady Nadine Heredia denied having any intent to evade or interfere with a money laundering probe and said a lower court's ruling to jail them before trial violated due process.

Humala and Heredia turned themselves in to authorities after the lower court's July 13 decision, which marked the second time that a former Peruvian president has been ordered jailed since Odebrecht admitted last year that it bribed local officials over three presidencies.

Ex-President Alejandro Toledo, believed to be in the United States, has refused to turn himself in.

"We ask this courtroom for a just decision because we stayed in our country and we plan to face this process in our country," Humala told the appeals court from jail via videoconference.

Peru's former President Ollanta Humala, and his wife Nadine Heredia, who are under preventative detention, attend a court hearing via video link, in Lima, Peru, July 31, 2017.

Prosecutor Rafael Vela said Humala should not be given special treatment for being a former president.

Unlike Toledo, Humala is not accused of taking bribes from Odebrecht in exchange for lucrative contracts. Instead, prosecutors allege that Humala and Heredia took $3 million in campaign funds from Odebrecht that the company had obtained illicitly and that the couple used for personal enrichment.

The couple denies taking any money from Odebrecht, said defense attorney Wilfredo Pedraza, who added that if they had it would be an electoral infraction but not a criminal defense.

The three-member appeals panel is expected to decide whether to overturn the lower court's ruling this week.

Freeing Humala and Heredia would mark a rare reversal in Peru's judicial system that has preventively detained at least five people so far in connection with Odebrecht.

So-called preventive prison before trial is somewhat common in Peru and has been criticized by some as overused or unfair.

In Brazil, pre-trial detention has been used to secure confessions from dozens of suspects in the Car Wash graft scandal involving Odebrecht.

Brazilian President Luiz Inacio Lula da Silva, who once championed Humala, has been sentenced to nearly 10 years in prison for graft but is free on appeal.

Toledo denies wrongdoing and is not sought for arrest in the United States because authorities there have asked Peru for more evidence.